The network statement

Remember the network statements are meant to identify which interfaces will participate in the Routing Protocol Process. It does not identify which networks to advertise rather which interfaces should participate in routing protocols process. So always think interfaces.

For example the network statement network 192.168.20.0 informs the RIP Routing Process to include any interface that falls in the range of 192.168.20.0 /24. Since RIP is a classful routing protocol it will apply the default major network prefix-length to the configured network address and will include all interfaces within that range.

Now let’s have a look at the show ip protocols and show ip route commands to see what has changed on R1.

RIP Metric

Uses hop count as the only metric.

Each hop in the path is assigned a value of 1. When a routing advertisement is received for a destination network, the router adds 1 to the metric value specified in the advertisement and specifies the sender as the next-hop.

A directly connected network metric = 0

Unreachable network metric = 16

Let’s examine

R 192.168.40.0/24 [120/2] via 192.168.20.2, 00:00:01, FastEthernet0/1

“R” signifies this is a RIP route.

“192.168.40.0/24” identifies the destination network.

[120/2] signifies the RIP administrative distance.

Then [120/2] states the network 192.168.40.0/24 is 2 hops away from R1.

The next-hop to reach the network is R2(192.168.20.2).

Finally, the egress interface to reach the next-hop is FastEthernet0/1.

RIP Timers

Route update timer (30s): Updates are sent every 30 seconds and when there are topology changes.

Invalid after timer (180s): Length of time that must pass before concluding a route is invalid

Hold Down timer (180s): If a router doesn’t receive an update from another neighboring router within the Hold Down time period or more, the receiving router marks all routes from the neighboring router as unusable.

Flushed after timer (240s): If there is still no update after 240 seconds, the receiving router removes all routing table entries for the neighboring router that failed to send an update.

R1#show ip protocols
*** IP Routing is NSF aware ***
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 17 seconds
!--- The time between routing updates ---!Invalid after 180 seconds, hold down 180, flushed after 240!--- The timer vales for invalid, hold-down and flushed ---!
Redistributing: rip
Default version control: send version 1, receive any version